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Executing a sequence of commands as a single background process

 
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# 1  
Old 10-02-2009
Executing a sequence of commands as a single background process
I'm writing a PHP script which will take a given media file and convert it into a flash (flv) file. In addition to this, once the flv file has been generated I create two thumbnails (of different sizes) from the newly generated flv file.

In order to do this I'm calling ffmpeg from the command line with the following 3 calls:

1. Generate the flv from the mpg
Code:
/usr/bin/ffmpeg -i /home/.../input.mpg -ar 22050 -ab 64k -b 400k -r 25 -f flv -y -s 304x240 -padright 8 -padleft 8 /home/.../output.flv >> /home/.../log.txt 2>&1

2. Generate the 'lrg' thumbnail
Code:
/usr/bin/ffmpeg -i /home/.../output.flv -f mjpeg -y -s 320x240 -vframes 1 -ss 8 -qscale 6 -an /home/.../thumb-lrg.jpg >> /home/.../log.txt 2>&1

3. Generate the 'sml' thumbnail
Code:
/usr/bin/ffmpeg -i /home/.../output.flv -f mjpeg -y -s 100x74 -vframes 1 -ss 8 -qscale 6 -an /home/.../thumb-sml.jpg >> /home/.../log.txt 2>&1

Note that the 2nd and 3rd thumbnail generation commands rely on the output flv file generated by the 1st command.

These commands are all working fine if I execute them individually. However I would like to combine them into a single command which can be executed in the background. The reason for this is to allow me to pass this to the server via the php exec() function.

Searching around I believe I can do this by adding semi-colons between the commands and adding a ampersand to the end of the final command.

I've tried running this directly through the terminal using the following command (this is fairly lengthly...)

Code:
/usr/bin/ffmpeg -i /home/atw90m/public_html/ffmpeg_test/DELTA.MPG -ar 22050 -ab 64k -b 400k -r 25 -f flv -y -s 304x240 -padright 8 -padleft 8 /home/atw90m/public_html/ffmpeg_test/20091002144718.flv >> /home/atw90m/public_html/ffmpeg_test/20091002144718-ffmpeg.txt 2>&1;

/usr/bin/ffmpeg -i /home/atw90m/public_html/ffmpeg_test/20091002144718.flv -f mjpeg -y -s 320x240 -vframes 1 -ss 8 -qscale 6 -an /home/atw90m/public_html/ffmpeg_test/20091002144718-lrg.jpg >> /home/atw90m/public_html/ffmpeg_test/20091002144718-ffmpeg.txt 2>&1;

/usr/bin/ffmpeg -i /home/atw90m/public_html/ffmpeg_test/20091002144718.flv -f mjpeg -y -s 100x74 -vframes 1 -ss 8 -qscale 6 -an /home/atw90m/public_html/ffmpeg_test/20091002144718-sml.jpg >> /home/atw90m/public_html/ffmpeg_test/20091002144718-ffmpeg.txt 2>&1 &

When I execute this however, only the first two commands appear get fully executed.
Reading the log file, the final command appears to stop mid-way through.

Can you see what I'm doing wrong here?


thanks for your help
Last edited by phatphug; 10-02-2009 at 11:27 AM.. Reason: Clearer formatting
# 2  
Old 10-02-2009
Hi.

(prog1; prog2; prog3) &

should do the trick. In case not, could you please reformat your post to use code tags? Thanks.
# 3  
Old 10-02-2009
Thanks for your reply scottn.

When I try that the first command fails to execute properly.

In normal operation the log would look something like:
Code:
Stream mapping:
  Stream #0.0 -> #0.0
Press [q] to stop encoding
frame=  210 fps=  0 q=3.5 Lsize=     563kB time=8.40 bitrate= 549.4kbits/s    
video:560kB audio:0kB global headers:0kB muxing overhead 0.618644%

With the brackets the log file ends after the "Press [q] ..." message

Code:
Stream mapping:
  Stream #0.0 -> #0.0
Press [q] to stop encoding

# 4  
Old 10-02-2009
Hi.

I'm not sure why that might happen.

Either try:
Code:
prog1 && prog2 && prog3 &

Or, failing that, put the three commands into a script
Code:
prog1
prog2
prog3

And run the script with &
# 5  
Old 10-02-2009
The &&'s had the same problem as the brackets.
It did work when running via a script though.

Strangely, when calling exec() in php with brackets around the 3 commands they do work. I'm not sure why the same doesn't work in terminal, but since I only need a working solution in php, this will do me.

Thanks for your help scottn.
 
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